Tafseer
{ فذلك } أي وقت النقر { يومئذ } بدل مما قبله المبتدأ وبني لإضافته إلى غير متمكن وخبر المبتدأ { يوم عسير } والعامل في إذا ما دلت عليه الجملة اشتد الأمر.
{That} meaning the time of the knocking {on that day} is a substitute for what preceded it, the subject, and it was built because it was added to something that was not established, and the predicate of the subject is {a difficult day}, and the factor in if is what the sentence indicates, the matter becomes difficult.
